by Denise Croote '16
Middle school, commonly known as the period that abruptly ends every mother’s obsession with family photos, is also a time loaded with an irrational desire to look “cool.” Common scenario number one: the teacher’s back is to the class when a craaaaaack pierces the silence, followed by an eruption of contagious giggles. With a stern look on her face the teacher dramatically whirls around and dives into a well-rehearsed rant about how we are all destined for a life plagued with osteoarthritis if we continue to crack our knuckles. Though it is undeniably annoying, second only to pen clicking on a scale of unnecessary vexatious behaviors, knuckle cracking has not actually been found to increase risk for osteoarthritis.
25% to 54% of people habitually crack their knuckles. That is, they manipulate their finger joints to produce an audible crack. The crack immediately releases joint tension and increases the joint’s range of motion, which is why people are so enthralled by it. When beginning the behavior, a person will pull on their joint to lengthen it, subsequently decreasing the pressure inside the joint. The decrease in pressure causes microscopic gas bubbles in the synovial fluid (the fluid filling the space between the bones) to expand and form a large bubble. As the person continues to lengthen their joint space, which can be done up to three times the baseline, joint fluid flows into the newly created area and causes the larger bubble to collapse back into the microscopic bubbles. This collapse coincides with the cracking noise and the maneuver leaves the joint space and fluid more evenly distributed. It typically takes at least fifteen minutes for the joint to be capable of being cracked again because the microscopic bubbles must dissolve and the joint space must retract to its resting position.
In vitro studies have measured the amount of force required to crack a knuckle and have concluded that the force exceeds the energy threshold required to damage articular cartilage, which lines the bones of the joint. Therefore, it would seem logical that chronic knuckle cracking would gradually thin articular cartilage. However, there is no scientific evidence for this claim. A Medline search revealed a study that looked at 300 randomly selected persons above age 45. Although those who cracked their knuckles were more likely to have swollen hands and demonstrated a reduction in grip strength, the prevalence of osteoarthritis was the same for both the cracking and the non-cracking groups. Further, a study in a nursing home investigated the prevalence of osteoarthritis among 28 residents. Six identified themselves as knuckle crackers. Interestingly, the prevalence of osteoarthritis was significantly higher in the non-knuckle cracking group than it was in the knuckle cracking group. However, these studies did not quantify the duration or frequency of knuckle cracking.
To better address this misconception, a retrospective case-control study examining knuckle-cracking behavior in a population ages 50 to 89 was conducted. This study included 135 people with osteoarthritis and 80 healthy controls. The prevalence of knuckle cracking was the same in both groups. In order to quantify the amount of knuckle cracking a person engaged in, participants estimated how many times they cracked their knuckles per day and how long (in years) they had been cracking their knuckles. Overall, they still did not find any association between knuckle cracking and osteoarthritis.
Though knuckle cracking does not correlate with the risk of osteoarthritis, it has been shown to increase the likelihood of having swollen hands and to reduce grip strength later in life. Nearly 85% of people in the previously mentioned study that examined knuckle cracking had swollen hands, compared to only 6% of people in the non-knuckle cracking group. Knuckle crackers in this study also showed a reduction in grip strength by 25% when compared to that of non-knuckle crackers. All in all, are the things we do in middle school to look cool worth it? Most likely not, but if they provide nothing else, they certainly give us something on which to look back and laugh.